Thin-wall radome utilizing irregularly spaced and curved conductive reinforcing ribs obviating side-lobe formation



"June 12, 1962 CONDUCTIVE RIBS A. F. KAY

THIN-WALL RADOME UTILIZING IRREGULARLY SPACED AND CURVED CONDUCTIVEREINFORCING RIBS OBVIATING SIDE-LOBE FORMATION Filed D90. 5, 1958 2Sheets-Sheet 1 IRREGULARLY CURVED AND SPACED RADIO WAVE TRANSPARENTINVENTOR.

June 12, 1962 A. F. KAY 3,039,100

THIN-WALL RADOME UTILIZING IRREGULARLY SPACED AND CURVEID CONDUCTIVEREINFORCING RIBS OBVIATING SIDE-LOBE FORMATION 2 Sheets-Sheet 2 FiledDec. 3, 1958 INVENTOR. AM/v A Mr I BY MM Afivf/viff Pa -tented June 1 2,1962 The present invention relates to radomes for the housing andprotection of radar antennas and more particularly to radome structureshaving reinforcement members of a configuration which provides a maximumof structural strength with minimum interference with the desiredelectrical properties of the radome, and which members may beadditionally or alternatively used as a radio frequency antenna.

Conventional radomes are usually designed on the basis of a compromisebetween desired electrical and structuralproperties. For idealelectrical performance the beam of the radar antenna should be entirelyunaffected by the radome. No material in front of the radar antenna andhence no radome at all would be the most desirable electrical design.For structural reasons radomes are required both in airborne radar wherethe aerodynamic shape of the aircraft is of the utmost importance andalso in ground based radar where the antenna must be protected againstweather and wind loadmg.

Five common types of radomes in use today are (a) thin wall, (b)half-wave wall, multiple half-wave wall, (d) A-sandwich, and (2)multiple sandwich. (a), (b), and (0) above are homogeneous dielectricconstructions. (d) and (e) above are non-homogeneous structures.

Of the above structures the thin wall (thin compared to a wavelength)is, in general, electrically the most desirable of the homogeneouswalls. If the thin wall is not structurally adequate, a half-wave wallis the most desirable. If still further structural strength is required,a multiple half-wave wall (e.g. a full-wave wall, threehalves wavelengthwall, or the like) may be used. If alternatively a sandwich typeconstruction is to be employed the best electrical performance comes theA- sandwich comprising a three layered wall in which the middle layer isa foam 0r honeycomb of low relative dielectric constant (a valueapproximately equal to 1.2 forexample) which is covered on both sides bythin skins of higher dielectric constant (usually a fiber glasslaminate). If the sandwich construction is desired, and if theA-sandwich is unsatisfactory structurally, a multiple sandwich may beused consisting of 5, 7 or more layers. Whether the homogeneous or thesandwich construction is employed, in general the more layers that areused the poorer the electrical performance'and the better the strengthof the radome will be.

From the above description of the common practice in the-art ofconstruction of radomes it will be realized that the practice is to formthe radome from a wall of material either homogeneous'or non-homogeneouswhich is of suificient structural strength yet which provides a minimumofinterference with the electrical propagation from the antenna.

On the other hand, the present invention utilizes a radome wall which isin itself of insufficient structural strength. In conjunction with thiswall reinforcing elements are used which increase the structuralstrength of the radome to meet the specific requirements. Obviously fora given-structural requirement this procedure will enable the designerto utilize a thinner radome wall or a wall with a fewer number of layersand hence'to provide a wall with electrically superior characteristics.Although the reinforcing structure tends to degrade the performance ofthe unreinforced radome, the net result is an overall design that is abetter compromise between structural and electrical requirements thancould be realized without the use of reinforcement. Although the use ofreinforcement in general is well known from a structural standpoint,such techniques have not been widely used in the radome art due to thefact that many deleterious electrical effects are produced by theinclusion of reinforcing structures and it has previously not been knownhow to overcome or avoid these effects in such a way that the addedstructural strength would not be outweighed by deterioration of theelectrical properties of the radome.

This invention relates to the design of reinforcing members in a radomestructure so as to minimize their undesired electrical effects and makepossible radomes wherein the compromise of electrical and structuraldesign is superior to that of radomes without these reinforcing members.Various radome structures are illustrated; however, it should beappreciated that radomes for different applications will have differentstructural and electrical requirements which will in a large measuredetermine the particular type'of structure according to the principlesof the present invention which would be most suitable for a particularapplication. Structural and electrical requirements, the geometry of theantenna and of the radome, the wavelength or wavelengths at which theantenna is to be operated, the environmental conditions and variousother factors will affect the design of the radome.

Two major effects of the radome reinforcing structure must be overcomein order to provide a practical radome structure. The first of theseeffects is attenuation or loss of gain of'the antenna radome combinationdue to the presence of the frame or reinforcing structure. In thepresent invention the design of the reinforcing structure is such thatthe loss of gain is limited substantially to the percentage of the totalradome area blocked by the reinforcing structure. This may beaccomplished by maintaining the hole size not less than approximatelyone wavelength. Since the maximum permissible loss of gain due to thepresence of the reinforcing structuremay be of the order of ten tothirty percent, a structurally eflicient reinforcing structure mayreadily be constructed within the prescribed limits of area ofobstruction by constructing a reinforcing structure consisting of a meshwherein the holes or openings are large compared to the size of thereinforcing members.

A second problem in the use of reinforcing structure is that ofdirective scattering of energy incident upon the radome from eitherside. If the energy scattered by the reinforcing structure is scatteredmore or less uniformly in all directions then the only appreciableelectrical effect is the loss of antenna gain. As previously: explained,a certain amount of loss of antenna gain is acceptable in view of thefact that the radome wall may be made much thinner and therebycompensate by improved characteristics for any loss due to thereinforcing structure. On the other hand, if the scattering from thereinforcing structure is directive in one or more directions in'space,that is, if the scattering from a substantial number of reinforcingelements adds up in space at some observation point distant from thereinforcing structure in'one particular direction or directions, then anerror or aberration in the directivity' characteristics, generally inthe form of a side lobe, will be created. If the radome structure causesa substantial side lobe to be created it will seriously diminish theutility of the antenna, rendering it useless for many applications.

The present invention provides an arrangement of the reinforcingstructure which prevents directional scattering. This arrangement may bebriefly described as an irregular, non-periodic, and. preferablynon-linear arrangement of the members making up the mesh of thereinforcing structure. From the theory of linear arrays of radiators, itis well known that any set of scatterers which lie along a straight linein space add in phase in at least one direction in space if the spacingbetween neighboring elements exceeds a half wave-length. As previouslyexplained, the fact that the radiation from a linear array of radiatorsadds in phase in one direction means that such an array in the radomereinforcing structure would produce a side lobe in a particulardirection. The present invention provides an arrangement of thereinforcing structure which prevents this condition from arising andthus substantially eliminates the creation of any side lobes due to thepresence of the radome reinforcing structure.

In addition to the above-described features and advantages of thepresent invention it is also an object of the present invention toprovide a reinforcing structure for a radome which may be constructed ofeither a conductive material or a non-conductive material and isarranged in such a manner as to provide a maximum of structural strengthin the radome and at the same time to provide a minimum of interferencewith the desired electrical characteristics of the radome.

It is another object of the present invention to provide a reinforcingstructure for a radome which is arranged in such a fashion that thecreation of unwanted side lobes in the antenna beam pattern is avoided.

It is a further object of the present invention to provide a mesh-likestructure to be incorporated in a radome which may be formed ofconductive material and insulated from the remainder of an aircraft bodyto provide an antenna for a propagation of radio frequency waves withoutinterfering with the propagation of higher frequency radio waves throughthe radome structure.

Other objects and advantages will be apparent from a consideration ofthe following description in conjunction with the appended drawings, inwhich FIG. 1 is a perspective view of a teardrop-type radome structureshowing the shape of a mesh-type reinforcing structure incorporatedtherewith;

FIG. 2 is a perspective view of a shell-type radome structure showing indotted lines a reinforcing structure incorporated therewith;

FIG. 3 is a partially schematic cross sectional view of a cone-typeradome having circumferential reinforcing elements presented to show thedegree to which such elements obscure a beam of electromagnetic energywhich is propagated in the direction of the axis of the cone;

FIG. 4 is a partially schematic perspective view of a conical radomeincluding a reinforcing structure embodying principles of the presentinvention and which may me constructed of conductive material andutilized as a radio antenna; and

FIG. 5 is a perspective view of a spherical-type radome structureincorporating a reinforcing structure according to the presentinvention.

Referring now to the drawings and particularly to FIG. 1, a radomestructure 11 is shown which is of the tear-drop type. That is, it isdesigned in a tear-drop shape suitable to be mounted on the surface ofan aircraft where it will protrude therefrom and serve to house a radarantenna. The radome 11 comprises a wall 12 which may be formed of anyhomogeneous or nonhomogeneous material of suitable electrical anddielectric properties for the construction of a radome.

The wall 12 however is formed of a relatively thin material so that itdoes not have the required structural strength for a suitable radomestructure. A reinforcing structure 16 is provided to give addedstructural strength to the radome 11. The reinforcing structure 16includes a number of elements formed in the shape of rods, bars, stripsor the like and shaped into a mesh to form reinforcing structure 16. Abase 13 is provided surrounding the open end of the radome 11 andproviding a rigid means for attachment such as to an aircraft frame.

As shown in FIG. 1, a first group of reinforcing elements 14 is providedwhich are generally but not exactly parallel, and a second group ofreinforcing elements 15 is provided, these latter elements 15 beingplaced generally transverse to the first group of elements 14 over thesurface of the radome 11. The elements 14 and 15 are spaced asubstantially distance apart to form a meshlike structure having anumber of relatively large openings 17 generally having four sides.

For clarity, the radome 11 in FIG. 1 is presented as though thereinforcing structure 16 were superimposed on the exterior of the wall12 of the radome 11. In some cases this may be a desirable structure.However, in many cases the reinforcing structure 16 will be placed onthe interior of the radome wall 12 to allow a smooth exterior surface tobe presented to reduce air drag, particularly in the case of aircraftradomes. In other circumstances, it may be desired to place thereinforcing structure 16' between two or more radome walls 12, or tomold it into a radome wall. Combinations of the above arrangements couldalso be utilized if desired.

It should be noted in FIG. 1 that the arrangement of the reinforcingelements 14 and 15 can best be described as being irregular, the meaningof this term being made clearer below. As previously suggested, thisirregular arrangement is intentional and provides a structure whicheliminates substantially all side lobes in the antenna pattern whichmight otherwise result from the use of a reinforcing structure. Thereinforcing elements 14 and 15 may be constructed of metal or some otherconductive material, but in any case it is contemplated that thereinforcing elements 14 and 15 will be constructed of a material whichis selected primarily for its structural characteristics, and will thusnot provide optimum electrical transmission characteristics but will actas a scatterer for the electromagnetic radiation.

If the electromagnetic energy scattered by the reinforcing elements 14and 15 is scattered more or less uniformly in all directions then theonly appreciable electrical effect is the loss of antenna gain. Althoughthis loss is not desirable, if the transverse dimension of thereinforcing elements 14 and 15 is relatively small compared to that ofthe opening 17, the percentage loss of antenna gain will remain withinacceptable limits. If, however, the scattering of the reinforcingelements 14 and 15 is additive in one or more directions in space thenappreciable side lobes will be produced in the antenna pattern due tothe presence of the reinforcing structure 16. This effect is highlyundesirable and must be avoided if a practical radome structure is to beprovided.

The characteristics of the present arrangement of the reinforcingelements 14 and 15, which avoids the generation of antenna beam sidelobes, may be understood from the following analysis of the scatteringproblem. The scattering from the reinforcing elements 14 land 15 will bedirective if the scattered energy from a substantial number ofreinforcing elements 14 or 15 is additive in I phase at observationpoints distant from the radome 11 in one or more particular directionsfrom the radome 11. The reinforcing elements 14 and 15 may be consideredas a set of scatterers of electromagnetic energy. Since they arerelatively few in number and fairly well separated in space, theincident field at each scatterer is primarily the field of the originalradar beam from the antenna. In other words, the effect of multiplescattering can be neglected. It may thus be assumed that the phase ofthe scattered field due to each individual scatterer is the same as thephase of the incident field at the scatterer or differs from theincident field by a constant value. The far field pattern of thescattered field is a sum of a number of terms each one representing thescattered field of'one of the reinforcing elements 14 or 15. If theseterms add in phase in a particular direction in space, then a side lobewill occur in this direction.

From the theory of linear arrays of radiators it is known that any setof scatterers which lie along a straight line in space regardless of theorientation of this line must'necessarily add in phase in at least onedirection in space provided that the spacing between neighboringelements exceeds a half wave-length. In the reinforcing structure 16 thespacing between elements 14 and 15 is preferred to be not less thanapproximately one wavelength. Therefore, the spacing between neighboringelements and the reinforcing structure 16 exceeds a half wave-length andthus any rectilinear arrangement of any one element or group of elementsis to be avoided. A configuration of reinforcing elements 14 and 15 suchas that shown in FIG. 1 best approaches the condition wherein there isno set of scatterers which lie along a straight line in space.

Several characteristics of the shaping and arrangement of reinforcingelements 14 and 15 are responsible for this desirable condition. In FIG.1, and particularly in the case where reinforcing elements are manywavelengths long, these elements are not straight but are curved by asubstantial amount along each portion of their length. Preferably thecurvature of the reinforcing elements 14 and 15 is such that the curvecannot be contained in a single plane. That is, the curves should beskew, not plane curves. A more precise way of stating thischaracteristic of the reinforcing elements 14 and 15 is that they shouldbe formed in a curve with torsion bounded away from zero, that is,differing widely from zero. Torsion is sometimes called the secondcurvature and is a measure of the curvature out of the osculating planeat any point of a non-planar curve.

' Each of the reinforcing elements 14 and 15 should be shaped in a curvewhich has a torsion substantially different from zero throughout themajor portion of its length. This feature of the reinforcing structure16 is not absolutely necessary for the practice of the invention, butprovides an increased measure of effectiveness in that curves of theabove description which differ substantially from plane curves are ofsuch a nature that a set of such curves when placed together is notlikely to form a set of scatterers which lie along a straight line inspace. It will be understood that the term curve is usedherein in itsgeneral sense to include straight lines or series of straight linesegments, or series of curved segments, whether smoothly or angularlyjoined.

Anothercharacteristic of reinforcing structures such as-16 which isimportant in eliminating the possibility of antenna beam side lobes isthe characteristic of aperiodicity. In-other words, all periodic orregular meshes are to be avoided in the construction of the reinforcingstructure 16. This is'necessary due to the fact that any regular mesh orset of'elements arranged in repetitive or periodic fashion tends to haveone or more such sets of elements or portions of elements which arelinearly arranged in space. It is inherent in the nature of propagationof scatterer elements that a regular or periodic array of such elementstends to produce scattering which is morepronounced and in phase inparticular directions andthus to produce lobes in the radiation pattern.

From an examination of FIG. 1, it will be observed that the reinforcingstructure 16 possesses in a high degree all of the abovecharacteristics. The reinforcing elements 14 and 15 are not only curvedbut are formed in the shape of non-planar curves so that substantiallyevery portion of each of the elements '14 and 15 is formed in acurvewhich has -a torsion bounded away from zero. It will further be noted,that although the holes 17 in the structure 16 are approximately ofequal area (as is desirable for generally uniform reinforcing) thedimensions of these holes, and particularly the dimensions of adjacentholes, arenot similar. In fact, the dimensions of adjacent ones of theholes 17 or, in other words the spacing of adjacent scattering elements14 and 15, is designed to be dissimilar, insofar as is consistent withthe desirable feature of maintaining the hole '17 of approximately equalarea. In addition to the apertures or holes 17 differing from oneanother it will be observed that the holes formed by the reinforcingelements 14 and 15 are individually formed generally in the shape ofirregular rather than regular polygons and adjacent elements departsubstantially from parallelism. Strictly speaking, the holes 17 are notpolygons at all since they are bounded by curved lines.

Although the particular reinforcing structure 16, shown in FIG. 1, hasall of the previously described desired characteristics in a high degreeit will be appreciated that complete irregularity and nondinearity isdifficult to obtain practically, and particularly when it is desired toproduce the articles inexpensively and in relataively large numbers. Itshould be pointed out therefore that a certain amount of regularity inthe reinforcing structure 16 is tolerable, but it should always be keptin mind that the regularity, periodicity and linearity of the structure16 should be kept to a minimum.

In PEG. 2 an alternative shell-type form of radome structure 13 isshown. The radome structure 18 is formed generally in'the shape of ahalf cone. This'structure is relatively long and narrow and would derivesubstantial support from its adjacent structure along its point ofattachment and the edges of the radorne structure 18. in this case, andin other circumstances, it may often be unnecessary to providelongitudinal reinforcing members in the radome structure. Radomestructure 18 is therefore provided only with transverse reinforcingmembers 21. As in the case of FIG. 1, of course, a radiationtransparentwall 19 is provided which forms the body of the radome structure 18where the reinforcing members Zilare attached or imbedded.

The reinforcing elements 21 generally have the characteristics ofreinforcing elements 14 and 15 in FIG. 1 in that they are formed in theshape of non-planar curves. Since there are no longitudinal reinforcingelements there is no mesh as such in the embodiment of FIG. 2.. Thespacing of elements in FIG. 2 is therefore defined by the averagelongitudinal spacing bet-ween the elements 21 rather than by the area ofthe holes 17 as was the case in FIG. 1. It will be noted in FIG. 2 thatthe spacing between elements 21 is not exactly equal but is generally ofthe same magnitude. It is apparent therefore that the radome structure18 of FIG. 2 is a simplified form of the previously described structure16 which is particularly adapted to situations where the radome is of aparticular shape or in other special circumstances.

In certain radome applications the surface of the radome mustnecessarily form a relatively small angle with the direction ofpropagationo-f radio waves from the antenna. An example of such asituation is illustrated in FIG. 4 where a nose cone radome is shownsuch as might be utilized on supersonic airplanes or missiles. Where thesurface of the radome cannot be made substantially perpendicular to thedirection of propagation of the electromagnetic waves a problem ariseswhich may he explained by reference to FIG. 3.

In FIG. 3 a fragmentary cross-section of a conical radome is shownwherein the direction of the propagation of'the electromagnetic energyis indicated by the arrow A. The angle between the axis and surface ofthe radome is indicated by the symbol 6 and is illustrated as 15degrees. Assuming then, illustratively, that the reinforcing elements 20are spaced three inches apart and are approximately three-eighths of oneinch in diameter, it would appear that the ratio of opening size toelement size, namely three inches to three-eighth inches, would providea ratio of eight to one, and thus would produce very little attenuationof the signal. However, due to the fact that the direction ofpropagation of the electromagnetic energy is not substantiallyperpendicular to the radome waves but is at a relatively small angledegrees in this example) to the radome wall, the structure illustratedin FIG. 3 is, in fact, not suitable. This can be shown by taking thehorizontal projection of the elements 2% on a transverse plane BB, whereit will be seen that the center-to-center distance in this projection isonly three-quarters of one inch. If the element diameter is assumed tobe three-eighths of one inch the degree of obscuration due to thereinforcing elements 21 is increased to one-half for electromagneticwaves propagated in the direction of the radome axis as indicated by thearrow A.

The structure illustrated in FIG. 3 therefore brings out the fact thatwhere a radome is used having a small angle between the radome surfaceand direction of propagation, the spacing of reinforcing elements alongthis direction must be greatly increased due to the increasedobscuration of radiated energy of elements spaced along this direction.Fortunately, this increased spacing can be utilized without undulyweakening the reinforcing construction in most radome configurations.

In FIG. 4 for example, the conical radome requires relatively littlereinforcing around its periphery and the greatest reinforcement isrequired longitudinally of the radome due to its long slender shape. InFIG. 4 a radome 22 of generally conical shape is shown incorporating areinforcing structure which is generally similar in principle to thestructure of FIGS. 1 and 2 but is adapted to the conical shape of theradome 22. A radome wall 23 is shown in phantom lines in FIG. 4 toreveal the details of the reinforcing structure 34). As in the case ofthe previous radome structure the wall 23 can be placed inside oroutside the reinforcing structure 30, or

alternatively the reinforcing structure 30 can be built within theradome wall 23.

A number of generally longitudinal reinforcing elements 24 are providedwhich are curved so that they do not provide a linear array. Spaces 29are formed between the elements 24, which are large compared with thesize of the elements 24. Adjacent ones of the spaces 29 are preferablyof unequal size. This further increases the irregularity of thereinforcing structure 3% and prevents the formation of side lobes in theantenna beam pattern. As Was the case with previous structures thespaces 29 are preferably approximately equal to one wave-length orgreater. This spacing, together with the relatively large sizes of thespaces 29 compared to the elements 24, provides a structure wherein thedegree of attenuation of the signal is kept to a small value.

Transverse reinforcing elements 25, 26 and 27 are provided to join thelongitudinal elements 24 into a mesh-like reinforcing structure 30. Asexplained with reference to FIG. 3, it is desirable that the generallytransverse reinforcing elements 25, 26 and 27 be spaced much furtherapart than are the longitudinal elements 24. The factor by which theelements 25, 26 and 27 must be increased depends upon the angle betweenthe radome surface and the direction of wave propagation.

The transverse elements 25, 26 and 27 are also preferably formed in theshape of non-planar curves for maximum reduction of side lobe effect. Asin the previous structures, however, it should be understood that thedegree of reduction of side lobe depends on the overall design of thesystem and in many cases structures less than optimum from thisstandpoint can be utilized. In such a case a compromise for simplicityof construction can be made and the reinforcing elements 25, 26 and 27can be made in the shape of simple circles.

The reinforcing structure at the radome nose 31 is not shown but it willbe understood that the general configuration can be extended to a smallconical tip at the end of the radome nose 31. In some cases, it may bedesirable to reduce the number of longitudinally reinforcing elements 29as the nose 31 of the radome is approached. This may readily beaccomplished for example by eliminating alternate ones of thereinforcing elements 29 at the forward reinforcing element 25. Amodification of the structure of FIG. 4 can be made wherein the numberof longitudinal reinforcing elements 24 is also reduced in passingothers of the transverse reinforcing elements such as 26 and 27.

In some cases, it may be unnecessary to carry the reinforcing structure30 completely to the nose 31 of the radome so that the nose 31 of theradome may consist solely of the radome wall 23 without any reinforcingstructure 39.

In addition to the function of reinforcements, or in place of thisfunction, the structure 30 may be utilized as an antenna operating on afrequency lower than that of the radar antenna within the radome 22.Although the structure 3i) does not interfere with the radar propagationtherefrom to any appreciable extent, it will form an antenna forsomewhat lower frequency of propagation. A serious problem exists in thedesign of present day airplanes and missiles in providing a suitablecommunications antenna system without interfering with the aerodynamicintegrity of the aircraft. The use of a structure such as shown in FIG.4 provides an ideal solution to the problem in that the radome structuremay be utilized as an antenna, for communications for example, thuseliminating the difiieult job of building such an antenna into the wingtip or other portion of the aircraft.

An arrangement for utilizing the structure 30 in FIG. 4 for acommunications antenna is schematically illustrated. For this purposethe mounting ring 28 by which the radome 22 is secured to the aircraftbody (shown in phantom lines at 32) should be formed of a non-conductivematerial, or alternatively should be provided with a non-conductivesurface or otherwise arranged to insulate the frame of the aircraft body32 from the radome reinforcing structure 30. It is thereafter a simplematter to connect a radio transmitter, shown in block form at 33, sothat one terminal is connected to the reinforcing structure 30 by meansof electrical lead 34 and terminal 35. The radio transmitter 33 wouldalso be grounded by means of lead 36 to the frame of the aircraft body32.

In some cases, it might be desirable to utilize a structure such as 30for an antenna even though reinforcement of the radome 22 is notrequired. In such an arrangement it is possible to eliminate in part orsubstantially diminish the size of the elements 24, 25, 26 and 27, sincethey would no longer be reinforcing elements but would only be utilizedas antenna elements.

The previous suggested applications for reinforced radomes has been forairborne applications. The application of reinforced radomes is by nomeans limited to these uses, however. FIG. 5 illustrates a ground-basedradome which incorporates a reinforcing structure according to thepresent invention and particularly adapted to this type of radomestructure. Ground-based radomes generally have a diameter ofapproximately 20 to 60 feet. For such structures, it is generallypreferable to construct a radome at the radar site. In such casesparticularly, there are obvious advantages to the use of generallylinear reinforcing elements rather than to attempt to construct a radomereinforcing structure entirely of non-planar, curved elements. Althoughit is possible to construct a groundbased radome of non-planarcurvilinear elements, a preferred ground-based radome reinforcingstructure 46 is shown in FIG. 5 which utilizes primarily planar orlinear elements and yet retains the major advantages of the previouslyillustrated structures.

The radome 42 will generally be in the shape of a portion of a sphereequal to, or somewhat greater than a hemisphere. The radome wall 42 willthus have a gen- 9 erally circular base 48. It is contemplated that thereinforcing structure 46 will therefore provide all, or nearly all, ofthe structural strength of the radome so that the radome wall 23 may beformed of cloth or film such as Dacron, nylon or the like and simplyplaced over and secured to the reinforcing structure 46. Such astructure will provide obvious advantages-over air-inflated radomestructures or rigid fiberglass laminate'radome structures, particularlyin the'case where it is necessary to remove the wall or-cover, as forportability; By theuse of the reinforced radome of FIG. the radome cover43 may be replaced in temperate weather without any disruption of theradar system operation.

The reinforcing structure 46 is formed of approximately horizontalelements 44 and approximately. vertical elements 45. These elements arearranged to form a meshlike structure having openings 47. The openings47 generally have the same characteristics as the openings of thepreviously described reinforcing structures. That is, the size of theopening is approximately equal to one wave-length or larger and thedimensions of adjacent openings 47 are preferably unequal to provide anirregularspacing of the elements 44 and45'.

In the radome 42 a compromise is provided with respect to the non-linearand non-planar characteristics of the reinforcing elements. Offsets 49are formed at the junction of vertical and horizontal reinforcingelements and elsewhere in the structure so that virtually no reinforcingelement 44 or 45 is linear for a distance greater than approximately onewave-length. This configuration retains the primary advantages .of'thepreviously described non-linear structures for the most part andprovides a further practical advantage of allowing the use of linearelements in the construction of the radome 42.

As in the previous structures the size of the reinforcing elements 44and 45 compared wtih the size of the openings 47 will be proportioned toobtain the desired compromise between structural strength and electricalproperties. The transverse dimension of the reinforcing elements 44 and45 will generally not exceed to 30% of element spacing. Since thesurface of the radome 42 is generally transverse to the direction ofpropagation of Waves therefrom the problem of increasing spacing discussed in connection with FIGS. 3 and 4 does not arise From theforegoing explanation it will be observed that a radome structure hasbeen provided which acquires a substantial portion of its structuralstrength from a re inforcing structure, which is of such a configurationthat attenuation and side lobe effects due to the reinforcing structurewill be within limits of toleration. Furthermore, such a structure, ifformed of a conductive ma terial, can be utilized as an antennastructure in addition to, or instead of, a reinforcing structure.

Certain variations and modifications of the illustrated embodiments havebeen suggested in the foregoing description. However, many modificationscan be made to the suggested embodiments by those skilled in the artwithout departing from the spirit of the present invention. The scope ofthe present invention is therefore not to be construed to be limited tothe embodiments shown and suggested but is to be limited solely by theappended claims.

What is claimed is:

1. A combined radome and antenna structure comprising a radome wall, anetwork of elongated conductive elements of small cross section comparedto their spacing united with said Wall, said elements beingsubstantially aperiodically spaced with minimum spacing of not less thanapproximately one Wavelength at the minimum operating frequency of theradome, each of said elements being shaped so that no portion thereof ofgreater length than approximately one wavelength at the maximumoperating frequency of the radome is in the form of a continuous planarcurve, and means for electrically 1'0- connecting radio frequencyelectrical signal means to said conductive elements.

2. A combined radome and antenna structure comprising a radome wall, anarrangement of elongated conductive elements united with said wall, saidelements being substantially aperiodically spaced withminimum spacing ofnot less than approximately one wavelength :at the minimum operatingfrequency of the radome, eachof said elements being'shaped so that noportion thereof of greater length than approximately one wavelength-atthe maximum operating frequency of the radome is linear and continuous,and means for electrically connecting radio frequency electrical signalutilizationmeans to said conductive elements.

3. A combined radone and'antenna structure comprising a radome wall, anarrangement of elongated conductive elements united with said Wall, andmeans for electrically connecting radio frequency electrical signalutilization means to said conductive elements.

4. A radome reinforcing structure for a radome for radar or similarapparatus having a predetermined range of operating frequencies, saidstructure comprising a network of conductive elongated reinforcingelements spaced aperiodically to form interstices having a dimensionofat least approximately one wavelength at the minimumoperatingfrequency of said apparatus, said elements having a relatively smallcross section compared to the aperture diameter of the antenna, each ofsaid elements being formed in the shape of a curve with torsion unequalto zero at substantially all points along its length.

5. A combined radome and antenna structure comprising a radome wall, anarrangement of elongated conductive elements united with said wall, saidelements being spaced with minimum spacing of not less thanapproximately one vvavelength at the minimum operating frequency of theradome, and means for electrically connecting a radio receiver ortransmitter means to said conductive elements.

6. A radome reinforcing structure for a radome for radar or similarapparatus having a predetermined range of operating frequencies, saidstructure comprising an array of conductive elongated reinforcingelements formed of electromagnetic radiation-scattering material spacedat least approximately one wavelength apart at the minimum operatingfrequency of said apparatus, each of said elements having no portionwhich is linear and continuous for more than one Wavelength of themaximum operating frequency of said apparatus.

7. A radome reinforcing structure for a radome for radar or similarapparatus having a predetermined range of operating frequencies, saidstructure comprising a network of conductive elongated reinforcingelements spaced aperiodically to form interstices having a dimension ofat least approximately one wavelengthat the minimum operating frequencyof said apparatus.

8. A radome reinforcing structure for a radome for radar or similarapparatus having a predetermined range of operating frequencies, saidstructure comprising an array of conductive elongated reinforcingelements spaced aperiodically at least approximately one wavelengthapart at the minimum operating frequency of said apparatus.

9. A combined radome and antenna structure comprisutilization ing aradome wall, an arrangement of elongated conductive elementsunited withsaid wall, each of said elements being shaped so that no portion thereofof greater length than approximately one wavelength at the maximumoeprating frequency of the radome is continuously linear, and means forelectrically connecting radio frequency electrical signal utilizationmeans to said conductive elements.

10. A radome reinforcing structure for a radome for radar or similarapparatus having a predetermined range of operating frequencies, saidstructure comprising an arrangement of elongated reinforcing elements,each of said 1 1 elements being formed of electromagneticradiation-scattering material and shaped so that no portion thereof ofgreater length than approximately one wavelength at the maximumoperating frequency of said apparatus is in the form of a continuousplanar curve.

11. A radome reinforcing structure for a radome for radar or similarapparatus having a predetermined range of operating frequencies, saidstructure comprising an irregular arrangement of elongated reinforcingelements, each of said elements being formed of electromagneticradiation-scattering material and having no portion which is linear andcontinuous for more than one wavelength of the maximum operatingfrequency of said apparatus.

12. A combined radome and antenna structure comprising a radome wall, anarrangement of elongated conductive elements united with said Wall, saidelements being substantially aperiodically spaced, and means forelectrically connecting radio frequency electrical signal utilizationmeans to said conductive elements.

13. A radome reinforcing structure for a radome for radar or similarapparatus having a predetermined range of operating frequencies, saidstructure comprising an irregular arrangement of elongated reinforcingelements formed of electromagnetic radiation-scattering material withsubstantially aperiodic spacing, each of said elements having no portionwhich is linear and continuous for more than one wavelength of themaximum operating frequency of said apparatus.

14. A radome structure comprising an irregular arrangement of elongatedreinforcing elements formed of electromagnetic radiation-scatteringmaterial with substantially aperiodic spacing, said elements defining aplurality of spaces of irregular form, whereby the scattering of radiofrequency energy from said reinforcing elements will be suflicientlyrandom to avoid the formation of side lobes in the pattern of adirectional antenna associated with the radome.

15. A radome comprising an array of conductive elongated reinforcingelements spaced at least approximately one Wavelength apart at theminimum operating frequency of the radome, each of said elements havingno portion which is linear and continuous for more than one wavelengthof the maximum operating frequency of the radome and a radio frequencyradiation transparent wall united with said array.

16. A radome comprising an array of conductive elongated reinforcingelements spaced aperiodically at least approximately one wavelengthapart at the minimum operating frequency of the radome and a radiofrequency radiation transparent wall united with said array.

References Cited in the file of this patent UNITED STATES PATENTS2,160,047 Wiggins May 30, 1939 2,607,009 Atfel Aug. 12, 1952 2,712,604Thomas et al July 5, 1955 OTHER REFERENCES IRE Convention Record, 1956,Part 1, vol. 4, page 237, March 22, 1956.

Analysis of the Electrical Characteristics of Structurally SupportedRadomes, Dept. of Electrical Eng, Ohio State Univ. Research Foundation,Columbus 10, Ohio, Nov. 15, 1958, pp. 1-90 (only pp. 56, 62, 77, 78, and89 relied on).

